Conventionally, in image viewing displays, such as LCD, an indoor lighting such as a fluorescent light, or incidence from sunlight from windows, or a reflection of operator's shadow etc. given to the viewing display surface sometimes aggravates visibility of pictures. Therefore, a light-diffusing layer is provided, on display surface, in which minute unevenness structure showing antiglare property, formed in order to diffuse a surface reflected light, to stop a regular reflection of outdoor daylight and to prevent a reflection of outside environment for the purpose of improvement in the visibility of images. As a formation method of light-diffusing layer, a method is mainly used in which a resin layer is formed from a coated layer having a resin containing fine-particles in dispersed state on a transparent film, because fine structure may be easily realized and at the same time excellent productivity may be realized by the method.
In a case of application to a high definition LCD, however, only mounting a sheet with the light-diffusing layer has caused problems that a portion (glittering) of strong and weak brightness combined is generated on a display surface and that surface reflected light excessively diffuses to thereby whiten a screen image (whitening).
In order to reduce such phenomena, a method has been proposed in which internal diffusibility and surface diffusibility are controlled. Described, for example, in JP-A No. 11-305010 is that a surface haze value is controlled in the range of from 7 to 30% and an internal haze value is controlled in the range of 1 to 15%. A light-diffusing sheet with an internal haze value in the range has not been able to exert a sufficient glittering preventive effect. Further described therein is that if the sum of a surface haze value and internal haze value of the light-diffusing sheet exceeds 30 in the light-diffusing sheet, whitening of a screen image surface increases, and it has been difficult to provide a screen image excellent in both of a glittering preventive effect and a whitening preventive effect even if a surface haze value and internal haze value are adjusted in the respective ranges.
As transparent films on each of which a light-diffusing layer is formed, there have generally been used films made of materials excellent in transparency such as triacetyl cellulose, polyethylene terephthalate and polycarbonate. A triacetyl cellulose film low in birefringence is main stream as a transparent film used on a polarizing plate indispensable in an LCD.
A light-diffusing sheet having a triacetyl cellulose film on a surface of which a minute unevenness is formed, however, has had a problem that if the light-diffusing sheet is exposed to a humidified environment at a high temperature for a long time, the light-diffusing layer is peeled off or degenerates because of hydrolysis of the triacetyl cellulose film. Recently, a norbornene-based resin film has been used as a transparent film, whereas such a film is poor in adhesion to the resin coating layer, thereby causing formation of a light-diffusing layer thereon to be difficult.
It is an object of the present invention to provide a light-diffusing sheet exhibiting almost no birefringence and excellent in adhesion and durability.
It is an another object of the present invention to, even in a case of application to a high definition LCD, provide a light-diffusing sheet, suppressing a screen glittering phenomenon and whitening hardly seen while maintaining antiglareness, exhibiting almost no birefringence, and excellent in adhesion and durability.
Also it is an object of the present invention to provide an optical element having the light-diffusing sheet provided thereto, and further to provide an image viewing display using the optical element.